Reciprocating compressor



Feb. 29, 1944. R. c, WARNEKE EI'AL RECIPROCATINGJCOMPRESSOR Fi led Jan.26, 1943 Inyentors; Roman C. Warneke,

William L. Knaus, by Fan/1,7 C? Their Attorney.

?atented Feb. 29, 1944 STATES PAT 2,343,211 RECIPROCATING COMPRESSQRApplication January 26, 1943, SerialNo. (01. 74-44) 3 Claims.

This invention relates to reciprocating compressors, and particularly tothe reduction of noise in high speed compressors.

High speed compressors such as those employed in refrigerating machinesare frequently constructed with reciprocating pistons driven by cranksor eccentrics which overhang the crankshaft bearing. At high speedsvibrations occur which may produce noise and become objectionable, eventhough they are not accompanied by undue wear of the mechanism. Amongother things, it hasbeen found that slight changes in alignment of theconnection rod bearing and crankpin during operation under load and dueto the bending of the crankpin may be a cause of objectionable noise.Accordingly, it is an object of this invention to provide areciprocating compressor having a piston driven through a connecting rodfrom an overhung crank and including an arrangement for minimizingvibration or noise produced by variations in alignment of the .crankpinand connecting rod bearing under load.

It is another object of this invention to provide a reciprocatingcompressor including a piston driven from an overhung crank'andincluding an improved arrangement for maintaining the connecting rodbearing and crankpin in alignment, regardless of changes in loadtransmitted through the connecting rod.

Further objects and advantages of this invention will become apparent asthe following description proceeds, and the features 01' novelty whichcharacterize the invention will be set forth with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to theaccompanying drawing in which Fig. 1 is a side elevation view in sectionof a refrigerant compressor embodying the invention; Fig. 2 is asectional view of the connecting rod of the compressor oi Fig. 1 on theline 2-2, and Fig. 3 is a diagram of the connecting rod having its bendunder load exag gerated for purposes of illustrating the theory ofoperation of the invention.

Briefly, the compressor illustrated in the drawing comprises acompressor crankcase and cylinder block, and the driving motor therefor,assembled as a unit. The compressor includes a reciprocating pistonwhich is connected to be driven by the motor through a crank overhangingthe bearing in which the motor shaft is journaled.

7 Under load, and particularly at high speeds, the bending of thecrankpin tends to produce changes in the alignmentmi the connecting rodbearing and the crankpin, and noise or vibration results. In order tomaintain thecrankpin and connecting rod bearing in alignment, regardlessof changes of load, the connecting rod is designed as an eccentriccolumn which bends under load in such a manner that the bearingisinclined at the same angle as the crankpin, and alignment is therebymaintained correct so that noise due to changes in alignment iseliminated.

Referring now to the drawing, the compressor shown in Fig. 1 includes acylinder block l0 and acasing or crankcase i I formed integrallytherewith and having a valve plate l2 and cylinder head 13 securedthereon. Within the cylinder block "I is provided a. cylinder H in whichis mounted a piston l5.v "Ifhe compressor is driven by an electricmotor, the frameof which is shown at I6 and which is secured by a pressfit or in any other suitable manner within the compressor casing II. Themotor I 6 includes agshaft l1 mounted in a suitable bearing 1 8andjhaying a crankpin l9 overhanging the bearing. 'I'he'piston I5 isconnected to th crankpin IQ for operation by a connecting rod 20 havinga bearing-2| engaging the crankpin, and a bearingZZ engaging agpvristpin 23 in the piston i 5. The connecting rod 20 is Journaled on thecrankpin l9 and pivotally secured to the piston, and the piston isreciprocated by rotation of the shaft ll. The compressor is providedwith a suitable intake valve, such as a flexible valve leaf 24, and witha suitable discharge valve which may be a similar flexible leaf 25.During th operation of the compressor refrigerant or other gas tobecompressed enters an intake chamber 26 in the compressor head l3 froman intake connection (not shown) and is drawn into the cylinder i4 abovethe piston l5. The piston l5 compresses and discharges the gas into achamber 2'! in the head l3 from which it passes through an outletopening 28 to be discharged from the compressor. A suitablecounterbalance 29 is provided on the shaft I! on the side opposite thecrankpin Hi.

In order to lubricate the moving parts of the compressor a splashingfinger 3G is provided which dips into a body of oil normally maintainedin the bottom of the crankcase formed by the easing II. The oil splashedupwardly falls into a reservoir 3| and reaches a bearing 18 through aduct 32. Oil also flows through a duct 33 within the bearing l8 betweenthe duct 32 and the end of the shaft and reaches an annular groove 34between the counter-weight 29 and the bearing structure. The edges ofthe bearing supporting structure are formed to provide an annularsealing face as indicated at 35, the seal cooperating with the face ofthe counter-balance 29. The effect of centrifugal force on the oilwithin the groove 34 causes a flow of oil through a duct 36 in thecrankpin, and a suitable porting groove 31 is connected to duct 36through a radial duct 38. Oil thus reaches the engaging surfaces betweenthe crankpin l9 and the bearing 2|. The porting groove 31 providescommunication between the duct 36 and an oil passage or duct 39 passingthrough the connecting rod 20, during that portion of the rotation ofthe crankpin when the force of the body of oil within the passage 39tends to cause the oil to flow toward the piston. A steady flow of oilis thereby produced due to the centrifugal force, and the force ofmomentum of the oil column in the duct 39, and the 011 thus reaches thepiston through a cross passage 40 in the wrist pin 23, and it reachesthe bearing 22 through a suitable opening ll in the wrist pin.

During the operation of the compressor under load, the crankpin I9 tendsto bend. The amount of bending is, of course, very slight and isimperceptible to the eye. However, at high speeds the bending of thecrankpin tends to change its alignment with the bearing 2| so that thebearing and pin do not remain parallel. Consequently, there is ashifting of the area at which pressure' is applied between the crankpinand the bearing and noise or vibration is produced. Objectionable noisemay occur, even though no undue wear of the bearing results.

In the compressor, as illustrated in the drawing, the connecting rod hasbeen designed as an eccentric column which bends under load in such amanner that the bearing 2| and crankpin l9 are maintained in alignmentthroughout variations in the load applied. The oil duct 39 connects thecenters of the bearings 2| and 22, however, the major portion of theconnecting rod 20 is at the left of the center line between the bearingsso that the load is applied eccentrically. The cross section of theconnecting rod is indicated at Fig. 2. The bending of the connecting rod20, which constitutes an eccentric column, is produced by the same forcewhichbends the crankpin l9 and is proportional thereto. When theconnecting rod 2|] is constructed in accordance with this invention,bearing 2| is maintained parallel with the connecting rod l9 so that thejournal and bearing remain in alignment regardless of changes in load inthe compressor. Noise produced by changes in alignment is, therefore,eliminated.

In Fig. 3 the bend in the connecting roq 2lD has been exaggerated forpurposes of illustrating the manner in which the dimensions of theconnecting rod are determined. The characteristics of eccentricallyloaded columns are well known, as

\ are also the characteristics of cantilever beams The connecting rod20, as has been indicated, constitutes an eccentrically loaded column;the crankpin i9 constitutes a loaded cantilever beam. The theory ofbeams and columns under stress is well established, and the necessaryformulas are readily available. It has been found that certainapproximations are useful in determining the dimensions of theconnecting rod of the compressor, such as that indicated at 20 in thedrawing, and the formulas given below are included as an illustration ofa method which may be useful in the design of the connecting rod.

then

M=bending moment E =modulus of elasticity I =area moment of section P=load a: =distance along beam y =distance at right angles to beam axis(deflection) For an eccentrically loaded column M=-P (y+e) where:

y=deflection e=eccentricity The eccentricity e of the connecting rod 20is purposely made large to minimize variations in manufacturing, and,since the rod must be relatively rigid, the deflection 1/ is smallrelatively to the eccentricity and can be neglected.

therefore:

EI g= Pe (approx.) integrating? y EI Pex-i- C (2) The column (connectingrod). is confined at its upper end where it is held between the'bossessupporting the wrist pin, at this end, as indicated in Fig. 3, 02:0 andtherefore 0:0 and dy EI f P893 and Equation 3 may be written El tan0=Pel (4) The slope (tan 0) of the crankpin under load may be determinedby actual measurement of the deflection or by calculation. Thecalculation of the deflection is complicated by the differences in thecross sections of the orankpin and the counterweight and by some bendingof the shaft within thebearing. A suitable graphical method fordetermining the deflection is suggested by A. E. Ault in ProductEngineering, vol. 2, No. 10, page 456. in an article entitled,Deflection in shafts of variable cmss section." This graphical method issometimes called Castiglianosmethod. The values of e and l aredetermined within fairly close limits by the particular compressor underconsideration; after tan 9 has been determined the connecting rodsection to establish the correct value of I can be determined inaccordance with standard design practice.

The solution obtained by the above equations is approximate as has beenindicated and a more I exact solution could be obtained if required.

However, satisfactory results can be obtained with the approximatesolution in many cases.

A compressor including a connecting rod constructed'in the manner setforth above may be operated at high speeds without noise or vibrationcaused by the bending of the crankpin under load. Since this bending isproportional to load,

' vibration due to the bending of the crankpin under load.

While the invention has been shown and described in connection with arefrigerant compressor, other applications will readily be apparent tothose skilled in the art. It is, therefore, not desired that theinvention be limited.,tp the particular construction shown anddescribed; and 1 it is intended in the appended claims to cover allmodifications within the spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a reciprocating compressor, a piston and a crankshaft, a bearingfor said crankshaft, a crankpin on said shaft overhanging said bearing,a connecting rod having a bearing joumaled on said crankpin forconnecting said piston to be driven by said crankshaft, said crankpintending to bend under load and said connecting rod constituting aneccentrically loaded,column having such cross section and length andeccentricity as to maintain the bearing on said connecting rod inalignment with said crankpin throughout variations in the load thereon.

2. A reciprocating compressor including :3. cylinder and a piston insaid cylinder, a crankshaft, a bearing for said crankshaft, a crankpinon said shaft overhanging said bearing whereby said crankpin tends tobend under load, and a relatively stiff connecting rod having bearingfor engaging said crankpin and said piston to drive said piston. saidconnecting rod being displaced longitudinally of said crankpin withrespect to the center line through its bearings whereby said connectingrod under load constitutes an eccentrically loaded column, the crosssection of said connecting rod and the eccentricity of said column andthe length thereof being selected so that the crankpin bearing on saidconnecting rod isinclined under load at the same angle as said crankpinto maintain said bearing and said crankpin in alignment throughoutvariations of load.

3. A reciprocating compressor including a cylinder and a piston in saidcylinder, a crankshaft. a bearing for said crankshaft, a crankpin onsaid shaft overhanging said bearing whereby said crankpin tends to bendunder load, a relatively stiff connecting rod having a crankpin bearingat one end and a piston bearing at the other, means for supplyinglubricant to said crankpin bearing, said connecting rod being displacedlongitudinally of said crankpin with respect to the center line throughsaid piston and crankpin bearings and having a lubricant conductingpassage along the center line between said bearings, said connecting rodconstituting an eccentrically loaded column having such eccentricity andlength and cross section that said crankpin bearing is inclined underload at the same angle as said crankpin to maintain said crankpinbearing and said crankpin in alignment throughout variations in load.

ROMAN C. WARNEKE. WILLIAM L. KNAUS.

